Radio signaling system



D. HINGS 2,395,049

Feb. 19, 1946.

RADIO SIGNALING SYSTEM 1 F iled Sept. 29, 1941 s Sheets-Sheef 1 INVENTOR ALTERNATING POTENTIAL BY SOURCE ATTORNEY Feb. 19, 1946. D. L. HINGS 2,395,049

' RAPIO SIGNALING SYSTEM I Filed Sept. 29, 1941 5 Sheets-Shed 2 DONALD L HINGS INVENTOR ATTORNEY FIG-.9

Feb. 19, 1946.

D. Hmes RADIO SIGNALING SYSTEM Filed Sept. 29, 1941 3 Sheets-Sheet 3 DONALD L.

HINGS INVENTOR ATTORNEY Patented'Feb. '19, 1946 V "Emma- G G 5 5511 53 Donald '"L. 'Hings, Ottawafiflntafiio, Canada, assignortolEle'ctronic Laboratories, lnc lndianapoli's', Ind at corporation o'f l'ndiana QApplicationiSeptember 29, 1941, Serial No. 11; 2}7:Q8

' .lmCanada. Octoher 1340 daemons. (019250-1 70 -fords voice :control act :the duration of Ythetransmission.2periods.

'My zimproved. carrier wave system embodies a :constantifrequency oscillator which is rendered operative :and inoperative 'by the operation of an aamplifier which .n'o'tonly serves as the modulator 'the iamplifier, but also automatically starts and stops the radio "frequency in the oscillator circuit, i thereby :eliminating the necessity T01? mechanical switches or' relays commonly used for this purpose. I alsoeliminate the necessity-for either a tuned circuit or else a radio frequency transformer in the ioscillator circuit, "and also eliminate the need of the intermediate amplifier stage commonly used asa buffer in the prior art practices ofcontrolgrid modulation. I also eliminate the necessity *of' shieldingtheoscillatorfrom the amplifier.

The constant frequency "oscillator includes a piezoelectriccrystal, and the invention automaticaflly controls the oscillator feedback potentials and excludes excessive currents fromfthe piezo electric crystal, thereby maintaining "the oscillator output in direct relation "with the control grid modulation requirements, as is in contradistinction'to the inverse relation which exists in ithe prior "art practice of :control grid modulation. In the'prio'r'art of control sri'd modulation ,foi a carrier wave, it is the conventional practice to shujnt connect the carrier wave'input of the amplifier with an interstage resonant circuit which is tuned tothe carrier, wave or some harmonic thereof, and to employ a. high frequency reactor as a bypass ibetween this tuned circuit and --zero potential or ground. 'Thisipractice requires tuning adjustments to be .made whenever the rir'equency of the carrier wave is altered. None of these prior art practices are necessary with-the presentinvention. It is also unnecessary itO resort to, the prior art practice ofv employing ,a radio i-requency transformer as. a coupling between the qsci l tora the am I In the prior art practiceof controlrgrid modulation, the output resonant circuit has -no;in'fluaddiiional amplifi r i also u p ied by a ndu ouplins'betr ee am ifiers- V i ,e p e e inven ion e arts .I TQ his p i .lpra'q ic .-.a acunverts t e am ifier i t a coupling ago that the resonance energy necessary .tordri-ve the ,amphfien'is deriyed irom the resonant oscillatory output circuit, instead of from an inductive :input circuit ,such as employed by the ipr r art.

31D. theipresent invention, the *input electrodes are reversed rinirelationtoatheprior art practices of control arid modulation and carrier -wave amplifier input. According to my invention, the carrier wave input fifrom itheioscillator is, applied to the cathode of the amplifier, and the modulating input is applied to the control grid 0f the amplifier, and this control grid is:maintainedat-aconstant zpotential irrespective -.'of the carrier wave ,irequency, and -.,there :is relatively low impedance between the rcathode and anode of the amplifier, so that the electron :fiow acts as a :coupling between :thentesonant oscillatory output circuit and the :oscillator'. :The' modulation is accomplished F by #varying the impedance ofithis coupling'or amplifier :tubej. That :isito say that the potential ch nges'occurring in the? low :frequency modulatinginput ato dihe control grid of the amplifier will alter :the impedance of Zthis coupling, thus altering the reactancel'betweenthemesonarit oscillatory output-:cirouit'and :the-ros'cillator, thu .gtlterin'g the teedhackin the-oscillator ,circuitand therebycontrolling theroutput of the" oscillatonand also affording a fast operating Bautomatic starting and stopping -0fth81g6118f2$i611 :periods of .the icarrier wave.

,-I n thisf rmanner, the invention provides a' simplified \control system which requires but a single resonant'circuit; andaaifords various degrees of amplitude {modulation which :may 'be either linear modulation, or else with variable Jnodulationsfactorsr :Voice control of (the :starting and stopping of .:the=generati'ongperiods rof the carrier wave qisgprovided with a minimum of equipment hereto-fore not considered :possible.

For interrupted continuous wave communications, the variations of the coupling of the invention, automatically interrupts the carrier' wave, at an audio frequency rate, to thereby produce the intended tone train, which may be keyed from a remote distance without the necessity of a keying relay; and dueto this coupling, the carrier wave is suppressed when the key is open, thereby affording the advantage of break-in operation, whenever occasion requires. tinuou wave communications, there is also provided the advantage of keying from a remote distance without the necessity of a keying relay, and the advantage of break-in operation whenever occasion requires. In either instance, there is afforded a high speed keying with exceptional clarity of the make and break tones.

The accompanying drawings diagrammatically illustrate the nature and principle of my invention. I

Fig. 1 is a diagram of the preferred form in which the invention has been reduced'to practice and is now in extensive use.

Figures 2, 3, and 4, show various control input circuits that may be used in operating my invention.

Fig. 2 shows a simple keying circuit, which may be employed when it is desired to operate my invention for keying carrier waves to produce space and marker impulses of continuous waves.

Fig. 3 shows a Well known circuit for operating my invention for modulation from a microphone.

Fig. 4 shows a well knowncircuit which may be employed when it is desired to operate my invention for keying interrupted continuous waves.

Fig. 5 shows a fragmentary view of Fig. 1, with an antenna connected to the output of the amplifier. V l

Figures 6, '7, 8, 9 and 10, show several charts of waves produced by the present invention. All charts indicate the transfer characteristics of the control tube and show the control potentials and their effect on the carrier wave amplitudes.

Fig. 11 shows an arrangement of amplifier tubes connected in cascade to the showing of Fig. 1. I.

Fig. 12 is a diagram of a single cathode embodiment of the invention.

The invention embodies a single resonant circuit which is the resonant oscillatory output from the amplifier which is here shown as a. beam type tetrode utilized as a coupling between the resonant oscillatory output circuit and the oscillator circuit. This beam tube is utilized as'a control grid modulator and amplifier, and the carrier 1 wave input from the oscillator is applied directly to the cathode of this beam tube which has'its control grid bypassed to ground for radio frequency and its screen grid at relatively constant potential. This prevents the amplifier from be coming regenerative and objectionably functioning as an oscillator, and'also provides for the carrier wave potentials in the resonant oscillatory output circuit to effectively control the oscillator circuit, so that the carrier wave input to the amplifier is in direct relation to the modulation requirements, and the output of the amplifier is thereby increased on the positive peak modulation. This provides an exceptionally efficient control grid modulation and als'o provides for resonant reactance between the utput of one amplifier and the input of a succeeding amplifier without the necessity of intervening resonant circuits which are essential in the'priorart of control grid modulation in order to enablethe For confirst amplifier to successfully excite a second amplifier.

If a triod is used in this manner the reactance of the anode electronically afiects the control grid and causes degeneration which impairs the sensitivity of the input. If a conventional tetrode is used in this manner, the screen grid functions as a shield and buffer electrode and absorbs the electronic changes, thereby defeating effective reactance to the cathode. Likewise, the conventional pentode presents the same inaptitudes to a greater extent when used in this manner. In the present invention, an entirely different function and greatly increased efficiency is obtained by using a beam, type tetrode as an amplifier and control grid modulator, with the carrier wave input to the cathode and with the control grid bypassed to ground for radio frequency and with the screen grid at relatively constant potential.

In this manner, the virtual cathode efiect of the beam tetrode is utilized to afford an eflicient resonant reactance between the output circuit of the amplifier and the cathode input thereof, whereby the resonant reactance energy necessary for operation of the amplifier is derived from the resonant oscillatory output circuit of the amplifier rather than from a resonant circuit preceding the input to the amplifier. It should also be noted that by applying the carrier wave input to the cathode instead of the control grid, alters the phase angle degrees between the amplifier output and the oscillator from what it would be if the carrier wave input were applied to the grid, with the result that the amplifier input is in direct phase relation to the feedback requirements of the oscillator. The amplificationand the coupling action of the tube are governed by the modulating voltages supplied to the control grid, and the coupling action directly affects the cathode-emission current which reacts in phase with and at the frequency of the carrier wave generator, to control the feedback thereof and alter the carrier wave output in direct relation to the modulation requirements. This performance affords various improved results which are not afforded by the prior art of control grid modulation wherein the carrier wave input is to the control grid of the modulator.

Fig. 1 diagrammatically illustrates the invention in the preferred form which has been reduced to practice and widely used. As here shown, two thermionic tubes are employed, V is in the control circuit and V is in the oscillator circuit. I have shown V as a beam tetrode, as that is the best form readily available for the purposeof my invention. The variable low capacity reactor 6 couples the anode 5 to one holder of the piezo crystal X, which has its opposite holder connected to the control grid 3. The negative potential is fed to this control grid through the resistor 1 which is interposed between this grid and the negative side of the biasing source S which has its" positive side connected to the cathode 2 which is connected to zero potential or ground. The biasing potential is here shown as a battery, but the Well known cathode bias may be employed. The positive potential to the anode 5 is fed through the high frequency choke coil 9. The screen grids 4 and I6 have a common connection to the positive potential, and are bypassed to the zero potential or ground, by the low frequency reactor 8.

The high frequency reactor H! couples the anode 5 to the cathode l4, and the high frequency choke coil ll connects the cathode M to the ins eels-.059

put terminal A and to the zero potentlalor ground terminal B is .connected .to the controlgrid 1.5 which 7 is bypassed to zero potential or. ground by the high frequency reactor I2, thusmakingthe anode to cathode return circuit of the oscillator tube V dynamically a part of the control circuit, and also making themodulatingand amplifying tubeV' dynamically a part ofthe oscillator circuit. This amplifyingtube :V' has beam electrodes, as indicated at D.

The .positivepotential to the anode 11 is fed through .the jnoneresonant .choke coil 18. The

high .frequency reactor 19 couples the anode l! with theinductance 2D whenan open oscillatory circuit is employed, otherwise this-reactor is may be omittedas it isonly for the purpose of potential isolation and safety, and is not essential for normal function. y

.A series resonant circuit may be provided by interposing the variable low capacity reactor 2| between the end of inductance 20 and the zero potential or ground. A low capacity reactor 22 may be connected between the inductance 20 and cathode 14 for the purpose of neutralizing the inter-electrode capacity of the modulator tube V, as is necessary for good linear modulation, but in some instances this reactor 22 maybe omitted when variable modulation factors are desired instead of good linear modulation.

The reactors 2| and 22'may both be omitted and an open oscillatory circuit employed, in

which case the antenna l3 as shown in Figure 5,

is attached by a switch I to the. inductance 20 which becomes a part thereof, as distinguished from the series resonant circuit in which the inductance 20 is coupled to any suitable output circuit in whatever mode may appearadvisable. It will be noted that theinvention does not employ the shunt resonant output circuit commonly used in the prior art.

From the foreging disclosure, it will be seen thatthe reactor l, cathode l4, control.grid l and reactor l2 form a return circuitbetween the anode I5and cathode 2 of the oscillator, thereby making the cathode l4 and control grid ii of the amplifier, dynamically a part of'the' oscillator circuit. The high frequencyreactor TI 2 bypasses the control grid Hi to ground and prevents changes in the cathode potential from altering the .potentialof this control grid; Thus the cathode emission current alternates in' phase with .andat the frequency of thecrystal X. The inductance is excited by the anode IT at the frequency of the crystal'X thus amplifying the high frequency wave. The cathode input impedance is high with relation to ground, and the anode output impedance is relatively low with relation to grid or ground, butthe cathode to anode impedance is low.

This cathode toanode impedance of the amplifieris variedby the modulating input supplied to the control grid J5, and the potential changes produced in the oscillatory output circuit alter the'dynamicpotentials on the anode ll with respect to the relatively constant potential on the screen grid 15 and thus there is established a coupling action which governs the cathode emissioncurrent of the amplifier V, so as to provide a closely linked relationship between the oscillatory output circuit and the oscillator circuit, so that the carrier wave potentialsin the oscillatory outputcircuit directly affect the feedback inthe s llator c r t an th eb -control the ut,-

put-of the. oscillatorin.directrelation :tothe modulation requirements. Due .to this coupling, the oscillatory output circuit: also supplies the cathode H with the resonant reactance fenergy which is essentially necessaryfor operation of theamplifier V. Furthermore, this coupling conveys power .fromthe oscillator V directly .to theoscillatory output circuit, thereby enabling the entire output oftheoscillator V to.-be utilized and also afiording v.a

.greaterefficiency of the amplifier V.

It will be seen .that this described coupling wouldbe impossibleif the carrier wave input was applied to the control grid l.5 instead of to the cathode I 4. That is to say that if the carrier wave input .was applied to the control grid .15, then the previously described coupling between the .resonant oscillatory output circuit and the oscillator circuit would .not exist, because such input to. the controlgrid would make the cathode a .partof the returncircuit of the amplifier output, :in. .contradistinction to the present invention wherein the cathode His excluded from the Ice turn circuit of the amplifier. output, and made the carrier waveinput of the amplifier, forthereason that the coupling action is always directly included in the cathode circuit rather than in the control grid circuitin which the grid is merely an operating electrode and not a conducting electrode asis the cathode.

Operation The invention affords an exceptionallyefiicient modulation overa wide range of amplitudes without ,the necessityiof any form of inductive conpling-between the oscillator and the amplifier. Changes in the modulating potentials supplied to the control grid l5 alter the dynamic impedanceof the beamtetrode V. and consequently alter .the couplin which controls the cathode emission current thereof, to thereby alter the feedback to the crystal, so as toproduce amplitude modulation of the oscillator output and also modulate the output of the amplifier, in direct accord with the variations of the modulating re,- quirements.

Theresonant oscillatory output circuit potentials form the basis of the coupling, and these potentials react upon the anode l1 and increase the dynamic potentials thereon, with respect to the relatively constant potential on the screen grid 16, thereby establishing the coupling between the anode I1 and the cathode M to therebyafiord an increased amplification of the os cillator output and consequently an increased amplification of the output of the resonant oscillatory output circuit. Thatis to say that the potential difilerences between the anode I1 and the screen grid 16 dynamically controls the .vertual cathode effect of the beam tetrode V so that the coupling alters the cathode emission current .of this amplifier in direct accord with the resonant frequency of the oscillatory output circuit, so as to thereby'increase the output of theoscillator circuit within which this amplifier cathode l4 isdynamically included,'as was-here:- inbefore explained.

At each negative cycle of the modulating ,potentials on the control grid 15, the impedance between the cathode M and anode I1 increases accordingly, therebyreducing the output .of the resonant oscillatory circuit and thus decreasing the effect of the coupling between the anode H and cathode J4 and consequently decreasing the :feedback' to .the crystal, thereby reducing the output from the oscillator'in accordance with the negative modulation requirements. When the coupling is at minimum, the oscillations of the crystal are then sustained by the normal feedback from the oscillator circuit.

At each positive cycle of the modulating potentials on the control grid l5, the impedance between the cathode l4 and anode ll is thereby reduced, and the output of the amplifier increases accordingly, which results in increased coupling action between the anode l1 and the cathode l4, thereby increasing the feedback to the crystal and thus increasing the output of the oscillator. This increased output of the oscillator increases the output of the amplifier in accordance with the positive modulation requirements. Thus it will be seen that this coupling provides a self-regulatory modulation which would be impossible with either an inductive coupling or a capacitive coupling.

The reactor 6 limits the feedback to the crystal, and whenever the mean potential of the modulating input becomes sufficiently positive to render the resonant oscillatory output circuit out of resonance with the frequency of the crystal, this out of resonance reactance will then oppose the existing feedback and promptly stop the crystal from oscillating. The maximum amplification of the carrier wave occurs just prior to the suppression of the oscillations and also at the initial input which starts the oscillator, thus assuring a fast operating control to start and stop the carrier wave generation.

The tube V serves the fourfold purpose of an amplifier, a modulator, a coupling, and a direct control for starting and stopping the oscillator generation periods of the carrier wave, and all of these functions are dependent upon the cathode emission current which is controlled by the modulating potentials supplied to the control rid l5.

It will be noted that the invention employs either an open oscillatory output circuit or else a series resonant output circuit, either of which afford a high reactance potential, which would not be obtained with a shunt resonant output circuit such as conventionally used in the prior art of control grid modulation. It should also be noted that with either the open oscillatory output circuit or the series resonant output circuit, there is no need for a return circuit or bypass to ground, such as would be required with a shunt resonant output circuit.

When the described open oscillatory output circuit is employed, it has the effect of a half wave antenna connected directly to the anode H, and there is high impedance between this anode I! and ground, thereby aifording exceptional efficiency without resort to a tuned input circuit such as used in the prior art. With this open oscillatory output circuit, the resonant period can be readily altered by merely altering the length of the antenna, as for instance by reeling or unreeling the antenna wire according to requirements. Whenever occasion necessitates changing the wave length, it is a simple matter to substitute a crystal of the required frequency and then alter the antenna length accordingly. This adaptability is of paramount importance in aircraft radio where cruising range sometimes gives rise to extreme conditions which would otherwise render operation exceedingly difficult or perhaps impossible. When for any reason, it is desired to alternately employ several crystals of different frequencies, it is a simple matter to quickly substitute one crystal for another and reel the antenna to correspond with the Wave length afforded by the crystal, there being no problem of a tuned circuit between the oscillator and-the amplifier, nor any shunt tuned circuit wit? antenna coupling, nor any output tank circui The invention may be operated in various modes with various control input circuits such as shown in Figures 2, 3, 4, and 5. The various performances of the carrier wave control are diagrammatically illustrated in Figures 6, 7, 8, 9 and 10, each of which show the control grid input voltage characteristics, with relation to the plate or output voltage characteristics. Each diagram indicates the transfer characteristics of the control tube V and shows the control potentials and their effect on the amplitudes of the carrier wave. For convenience of illustration, only one side band is shown in each instance.

Voice control here shown, the primary winding of the transformer 60 is connected in series with the battery El and the microphone 62. One end of the secondary winding of the transformer 60 is connected to the cathode 54 which is common to the terminal B. The low frequency reactor 59 couples the opposite end of this secondary winding to the diode plate 55 which is connected to the cathode 54 by the biasing resistor 58. The low frequency reactor 5! couples this diode plate 55 to the anode 5| which is common to the terminal A. The grid 53 is bypassed to the cathode 54 by the low frequency reactor 52, and this grid is also connected to the diode plate 55 by the grid resistor 56. The voltage dropping resistor 50 connects the cathode terminal B to the anode battery S which is connected to the terminal A.

When sound waves activate the microphone, the D. C. current from the battery BI is pulsated to excite the transformer 60. The resulting alternating potentials from the secondary winding of the transformer 60 are applied to the cathode 54 which is common to the terminal B, and also applied to the diode 55 through the reactor 59, and imposed on the terminal A through the reactor 51, thus producing the modulating potentials.

The potential changes on the diode 55 are rectified and the resulting current flowing between the cathode 54 and diode 55 produces a voltage drop across the resistor 58, thus making the diode 55 more negative in relation to the cathode 54. The grid 53 likewise becomes negative through the resistor 56, thus the normal current flow between the cathode 54 and the anode 5| is reduced by this increased negative grid bias, and the resulting decreased anode current reduces the normal voltage drop across resistor 50 and this reduction affords an increased potential from the battery S at the terminals A and B which provide the bias source for the control tube V. That is to say that the potential changes on the diode plate 55 produce an increased negative bias at the terminals A and B.

The grid 53 is bypassed by the reactor 52, so that no modulation is produced by this bias conassume:

When-these=modulating wavesareimposedonthe control grid IE" or the' 'amplifi'er V, thenegativebias is also imposed thereon; whereby t-he car rier wavegenerator 'v is renderew active and modulated carrier" wave thenexistsin the reso nanfioscillatoryoutput circuit. Whenthereare nofmodulating' waves; the oscillator: is inactive and the carrier vwaves'are suppressed; The arm plit'u'desof"themodulatinginput and the icompo nentr' bias inherent thereto efictually'governsthe; oscillator generation periods; and also controls the carrienwavele'vel" andth'eamplitudes of car rie'r-wave modulation; In this-manner," the;modf ulation' of the carrier wave. varies from-low"per== .c'entage -linear modulation. tor a high percentagemod'ulation' witlrextendedpositivepeals, depend.= in'gupon the-amplitude ofthe. m'odulating waves: and accompanying variable bias 'on' the;- control" rid I55 f For voice" control of theioperatin'g periods of the carrier wave-- and its W amplitude". m'odulatiom. the voice controlinput circuitof Fig. .11 is employed with either an open oscillatory circuit or with a series resonantcirouitwhichmay 'be either" with or without neutralization .of" the interel'e'c trode capacity, as circumstances: suggest". and necessityrequiresr.

Fig? 6" shows the performancewitha series" res; chant: circuit and=without interelectrode neutralization', whenthem'odulatihg waves are suppliech by'thevoice controlinputcircuit shown in Fig". 1;] and: illustrates overemodulation devoid of side band interference; The curve T indicatesnthe.

transfer characteristics of the-tube V" when. at;

fectedby interelect'rod'e capacity. which causes it. to deviate from" the" normahcurve indicated lily; the dotted line. The sine" wave W" indicates the,

variable input" amplitude, andthe line N indicates the corresponding variations. of negative bias... The sine curve; M indicates the varying amplitu'des' oi modulation of one side band, an'dlthe' dotted line Hindicates the mean carrier, Wave. amplitude whichis self regulatin iin accordance" with theimodulationpercentage. As hereshown the: oscillator generation; period starts when the negative bias" is imposed upon the control; grid and continues untilthe control.innut;.,definitely ceases and" the negative bias impulses are] no, longersupplied. Thus the carried'j wave) genera: tion period. is, started; andfstfoppea; by voice, com t'rol: A It will be noted that thetransfer characteristic of the tube is varied;:from:.the normal transfer characteristic,, thereby precluding the over modulated carrier' wave from: reaching zerof or" cut-,

olf onthenegativeimodulation peaks. This prevents sidebancf interference which would other.- wise occur'fi om over modulationgand makes pos siblean'over modulation far'in excessiofone him.- dredper-centandwithout the carrier wavereaching cut' ofi". This isof particular advantage in:

the transmission of weak signalsflwhichprequire excessive modulation to render them intelligible.-

Itiw-ill beseenthat-withthe simple-portableequipment: of my invention I accomplish results which,

would otherwise require considerable'equipment; When low percentagemodulation with good fidelity is desired the interelectrodecapacity may be neutralized by the. reactor 22 and the voice control inputcircuit. of Fig, 1. employed'for voice control'of the oscillator generation periods. This function is sufiicientl'y similar tov the showing in. a Fig. 6 that: further illustration is, .deemed unnecessary:

Linear modulation For linear modulation, the. control input circuit. of Fig: 3 may; be employed; with. the. described series resonant circuit, and for. maximum, lin.-. earity' of modulation, the interelectrod'e capacity. of the control tube Vshould be. neutralizedby, inverse feedback through the. reactor. 22; so as to. preventdistortion of the normalutransferl char-- acteristics; This performance. is. illustrated. in Fig; Q'LWhichshoWs. modulation- InsFig. 9; the curve T? indicates the normal transfer: characteristics. of. the. controltube, the,

sine wave Win'dicates themodulating inputwave, andthe sine wave M illustrates 100% modulation ,of'; the carrier wave, This, showing. need-not be furtheriexplained, audit. is shown principally fonwmparison. with the over modulation, of;-

Fig'. .10;

High percentage modulation For variable modulation. factors. in high. percentagemodulation, the ,input. circuit of. Fig. 3, is'used" withia series resonant circuit,v butwithout the reactor 22;. Thatlis. to say, linearity of the modulated wave formissacrificedfor greater positive peak. output. relative to the. unmodulatedcarrier wave. This, performance. is illustrated; in Ei'g..l0; V

In. Fig. 10, the. sine; wave windicatesjthemode ulatinginputwave; and. theitransfer characteristics .ofithe .control'tube are indicatedby thercurve- T until'it deviates .from.the truecurve shown by the dotted',-lihe.- Thisdeviat-ionl is duetorthe intenelectrode. capacity-and prevents the output.

carrier. wave, from. reaching. cut-ofi on zero on tion; or a wide range to input amplitudes.

' The resultsjof Figzlo'can, also be obtainedflwith airopen oscillatory circuit; and. in instances where there'is; occasion to change the frequency of'the carrier wave, it'isonlynecessary' to substitute a dilierent" crystal oithe required frequency-and t'o. alter'the antenna accordingly. This is of paramount advantage in aircraft radio where cruising range may give' rise to necessity for extreme changes in thecarrierwave. frequency andwhere tirnewouldnot permit'of extensive alterations be.- ing made to; convert the equipment from one frequency'toanother: This adaptability is due to latory circuit.

Continuous wave For continuous wave code transmission, the input circuit of Fig. 2 is employed, either with an open oscillatory circuit or with a series resonant circuit and either with or without the neutralizing reactor 22. This provides thermionic keying of the carrier wave generator or oscillator and affords considerably faster operation than direct keying of the carrier wave generator. That is to say that the invention provides a keying speed comparable to that of the well known bias keying of the amplifier, and also affords the advantage of break-in operation which unfortunately is absent in bias keying of the amplifier, unless resort is had to elaborate shielding of the oscillator circuit which is entirely unnecessary in the present invention. It should be mentioned that the use of the neutralizing reactor 22 makes it possible to more accurately control the feedback through the reactor 5 and thereby provide a more critical definition of the make and break, and in this way further enhance the speed of keying.

Fig. '7 shows the effect on the carrier ,wave when the control potential or bias is'varied relative to zero by the input circuit of Fig. 2. The carrier wave is non-existent until the key is pressed,-

whereupon the negative potential to the control grid l5 of the tube V starts the oscillator and maintains the generation of the carrier wave until the key is againopened, whereupon the'oscillator stops and the carrier wave ceases. A single pulse is indicated as illustrative of a marker wave in continuous Wave communications.

It will be noted that the greatest amplitude occurs at the make and break of the marker wave. This affords exceptionally well defined demarcations of the pulses and clarity of perception which is of paramount importance in high speed keying. This variation of amplitude within each pulse is obtained by operating the negative bias slightly in excess of the requirements for actuation of the oscillator, and this slight excess then slightly retards the output of the amplifier until the negaive bias swings back after the break to terminate the pulse with a rise in amplitude. Due to the thermionic actuation of the oscillator, the keying can be done from a remot distance without the necessity of a keying relay.

Interrupted continuous waves For interrupted continuous wave code transmission, the input circuit of Fig. 4 is employed, and

for this exceptionally high speed function it is advisable to employ a series resonant circuit with the neutralizing reactor 22. The tube V affords a thermioni control which automatically interrupts the carrier wave at an audio frequency rate to produce the intended tone train.

Fig. 8 shows the effect on the carrier wave when an audio frequency wave produced by the circuit shown in Fig. 4 varies the control potentials rela-- tive to zero bias. The carrier wave isalternately released and suppressed in accordance with the audio input wave, so as to produce a series of the illustrated pulses of the carrier wave. These p ses may be keyed in groups'for code transmission of the interrupted continuous wave variety and since the oscillator is suppressed when the key is open, there i also afforded the advantage of break-in operation whenever occasion requires. Due to the thermionic actuation of t e osc tor.

the keying can be done from a remote distance without the necessity of a keying relay,

Single cathode embodiment In Fig. 12 there is shown by way of example, a diagram which is explanatory of the fundamental principle of my invention. As here shown, there is enclosed within the tube V", a single cathode positioned between two anodes, and with a pair of grids intervening between each anode and the single cathode, and beam electrodes are provided as indicated at D.

In contradistinction to the showing in Fig. l

V the grounding is reversed in Fig. 12 so as to optive side connected to the single cathode 30. The, 7 high frequency reactor 38 bypasses the control grid 39 to the positive ground, and this control grid is connected to the input terminal B. The screen grids 32 and 40 have a common connection which is bypassed to the cathode 30 by the low frequency reactor 31 and also connected to the positive ground, preferably by the resistor 34.

The negative potential is fed to the single cathode 30 through the high frequency choke coil 36. The anode 4| is connected to the positive ground by the high frequency choke coil 44 and also connected to the inductance 42 which together with the illustrated antenna 43 constitutes the open oscillatory circuit.

In this single cathode embodiment, the anode 33, reactor 6', crystal X", grid 3| and cathode 30 form a high frequency oscillator circuit-wherein the. anode is at ground potential, and therefore the cathode potential alternates relative to the constant zero potential and in accordance with the frequency of the oscillations of the crystal X". This single cathode is therefore the output of the oscillator and also the input of the amplifier which embodies this single cathode 30, the control grid 39, the screen grid 40 and anode H. The high frequency reactor 38 bypasses the control grid 39 to ground and prevents changes in the cathode potential from altering the potential of this control grid 39, thus the potential of the control grid 39 is maintained at zero, while the potential of the cathode alternates at the frequency of the crystal X". The inductance 42 is excited by the anode 4| at the frequency of the crystal X", thus amplifying the high frequency wave.

The alternating and bias control potentials between the cathode and the control grid 39 are supplied through the terminals A and B by any selected control input circuit as before explained in the discussion of Fig. 1.

' Operation I The operation of thi single cathode emb0diment is the same as set forth under this caption in describing Fig. 1. The various performances of the carrier wave control are essentially the same as previously described in the discussion of the embodiment shown in Fig. l and are diagrammatically illustrated in Figures 6, 7, 8, 9 and 10. It will be readily understood that the illustrated open oscillatory circuit can readily be converted into a series resonant circuit as previously explained under Fig. 1, and either with or without interelectrode neutralization.

Multistage amplification The amplitude of the previously described carrier waves can be further amplified b the arrangement shown in Fig. 11 which shows an arrangement'of amplifier tubes connected in cascade to the showing of Fig. 1.

In Fig. 11 the first amplifier stage consists of two tubes V and V with all electrodes connected in parallel. The anodes ll-ll. are directly connected to the cathodes 26-26 of the tubes V -V which constitute the final amplifier stage. These amplifier tubes have beam electrodes as indicated at D. The screen grids 28-28 are connected to the source of positive potential through the potential reducing resistor 24. The anodes 29-29" are directlyconnected to the series resonant inductance 20. The positive potential is fed to the anodes 29-29 through choke coil 25 which is connected to the center of the inductance 20 to avoid being affected by high frequency voltage. The series resonating reactor 2| is connected between zero potential and the inductance 20 and the antenna I3 is. attached by a switch .l to the inductance 2i). The control input from the terminal A is fed to the cathodes 26-26 through the choke coil l8. The capacity of the cathodes 26-26 and anodes 29-29 is neutralized by the inverse feedback through reactor 22. and the control input from B is connected to the control grids 21-21 so as to make this final amplifier stage the controlled input amplifier and thus make it unnecessary to neutralize the inter-'- electrode capacity of the first amplifier stage.

These control grids 21-27 are bypassed to ground by the high frequency reactor l2, and the bias battery S is connected between ground and V the control grids l-5l5'.

The positive potential to the choke .coils 9 and i8 is fed through the potential reducing resistor 24; and the negative potential to the cathodes 26-26 is fed through the choke coil I8 from the potential reducing resistor 23.

The potential reducing resistors 23 and, 24 are used to divide the D. C. potentials to the correct values for the different tubes. The high frequency choke coil 25 performs the same function at the choke coil N3 of Fig. 1.

There is here shown a series fed series resonant circuit instead of the shunt fed series resonant circuit in Fig. 1; both are equally effective, but

the seriesfed circuit eliminates any need for the reactor I9 shown in Fig. 1. However, ashunt tuned resonant circuit is not satisfactory for the purpose of thermionic reactance, because .the're actance potentials are relatively low.

The tubes V and V are each rated at a much higher power than that ofeach of the tubes V and V so as to provide the intended power amplification.

It will be seen that the tubes" ii -V and V -V are connected in parallel and the groups in series. This series parallel arrangement of the four tubes provides approximately the same overall dynamic impedance between the oscillator and the series resonant output circuit asexisted in the tube V of Fig. 1; andthedescribed arrangement makes it possible to pyramid the amplification to many times that which would be afforded by Fig. land without any appreciable increase in the dynamic impedance.

Each of these amplifiers V V W and V provide a coupling, and the resonant 'reactance necessary to operate each of the amplifiers is supplied from the resonant oscillatory output airedit, and ithusthere is provided multistage amplification without any necessity for interstage circuits. These couplings enable the first am-' plifier stage to'convey its power to the final am-' plifier stage and therefore the total power is not merely the output of the final amplifier stage," butisalmost the sum total of both amplifier stages. That is to say, that in the absence of the coupling; the first amplifier stage would mereiy operate the final amplifier stage without conveying the primary amplification on to the final amplifier stage. Also, these couplings convey power from the oscillator V directly through eachof the amplifiers, thereby utilizing the entire out put of the oscillator.

The described parallel arrangement is for the purpose of overcoming the loss which would otherwise occur from the dynamic impedance which exists in the tubes now in general use,

and it will be readily understood that when suitthis lesser amount of equipment.

. It is readily conceivable to design a single tube to replace tubes V -V -V -V in Fig. 11, and thus make possible large amplifications of any Wave-form without coupling equipment, thereby resulting in a minimum of distortions as well as a minimum of equipment.

It should be mentioned that the screen grid 4- can be omitted from any of the Figures 1, or 11, as it is not absolutely essential to successful operation. It should also be mentioned that Fig. 1 and Fig. 11 are operatable within a restricted range without this reactor 6 which is preferentially included to enhance the range of utilization by selectively controlling the feedback according to conditions of operation, so as to assure efiicient stopping of the crystal oscilla tions. This intended purpose requires that the reactor 6 be of very low capacity, say less than 150 mmfd. as distinguished from the higher capacity reactors'whic'h are conventionally used for the purpose of isolation.

The reactors 8 and 31 have been described as low frequency reactors because that affords the most efii'cient operation; however, a suitable high frequency reactor will give satisfactory operation in either of these instances.

It should also be mentioned that in Fig. 1 when the inductance 20 is provided with an antenna; then the variable low capacity reactor 2| may be connected to the anode side of the inductance 2u'so as to equalize the antenna capacity to ground. This provides a greater carrier voltage on the antenna than at the anode I1 and affords a stronger signal on a relatively When this is done, the function is essentiallythe same as hereinbefore described, and would be similarly stated except that the term current would be used instead of the term potential, which is the language hereinbefore employed. This current regulating resistor is not essentially necessary for successful operation, and highly efii- V cient coupling can be obtained without it, however there are instances where it can be used to advantage.

It should also be mentioned that throughout the specification, the grid l6 has been termed a screen grid" in accordance with the conventionallanguage of the art; however, in the present invention, the grid l6 does not really function as a screen grid, but rather as a transmission electrode, which due to its precise linear alignment with the control grid, affords an adequate flow of electrons from the cathode to the anode and enables the potential changes which are produced on the anode by the reactance in the resonant oscillatory output circuit, to thereby create the coupling action within the amplifier and thus control the cathode emission current thereof. Thus it will be seen that in the present invention the grid It does not perform its usual function which is to shield or screen the oscillator circuit from the resonant oscillatory output circuit, but rather this grid l6 has decidedly the opposite effect and is of real importance in converting the beam tetrode into a coupling.

It is well known that a piezo electric crystal is the equivalent of an inductance and a capacitor shunted by a resistance, and therefore it is intended that this well known equivalent may be used in the present invention instead of the piezo electric crystal which has been mentioned in the specification merely for the convenience of description.

In the present disclosure I claim as my invention:

1. Apparatus for producing a signal modulated carrier frequency, comprising a space discharge device having at least an anode, a cathode and a control electrode, a source of carrier frequency for exciting the cathode withrespect to a point of reference potential, a load circuit including a series resonant circuit connected to the anode of said discharge device and energized by current appearing between said anode and said point, and means for applying modulating potentials to the control electrode of said discharge device.

2. Apparatus for producing a signal modulated carrier frequency, comprising a space discharge device having at least an anode, a cathode and a control electrode, a source of carrier frequency for exciting the cathode with respect to a point of reference potential, a load circuit including a series resonant circuit connected to the anode of said discharge device and energized by current appearing between said anode and said point, said series resonant circuit including an antenna having a distributed inductance and capacitance with respect to said point, and means for applying modulating potentials to the control electrode of said discharge device.

3. A radio frequency system comprising an impedance, a space discharge tube including an electron discharge path, a series resonant circuit havingtwo terminals and consisting of an inductor in series with a capacitor, means to effectively correct in series the impedance, electron discharge path and series resonant circuit, means to supply energy across the impedance at the frequency to which the series circuit is resonant, and means to connect a load between the junction of the inductor and capacitor and a terminal of the series resonant circuit.

4. A radio frequency circuit comprising, in combination, an oscillator tube having at least a cathode, an anode and a control element, a piezo-electric crystal included in a regenerative circuit connected between said anode and said control element, an amplifier tube having at least a cathode, an anode'and a control element, radio frequency connecting means including an aperiodic circuit for connecting the anode of the oscillator tube in the cathode-of said amplifier tube, means for connecting the cathode of the oscillator tube to a point of reference potential, a load circuit including a series resonant circuit connected to the anode of the amplifier tube and energized by current appearing between the anode of the amplifier tube and. the said point, and means for applying modulating potentials to the control electrode of said amplifier tube.

5. Apparatus for producing a signal modulated carrier frequency, comprising a space discharge device having at least an anode, a cathode element and a control element, means for connecting one of said elements to a point of reference potential, a source of radio frequency for energizing the other of said elements and thereby exciting the said anode at radio frequency potential with respect to said point, a load circuit including a series resonant circuit connected to said anode and energized by current appearing between the said anode and said point, and means for applying modulating potentials to one of said elements of said discharge device.

6. Apparatus for producing a signal modulated carrier frequency, comprising a space discharge device having at least an anode, a cathode element and a control element, means forconnecting one of said elements to a point of reference potential, a source of radio frequency for energizing the other of said elements and thereby exciting the said anode at radio frequency potential with respect to said point, a load circuit including a series resonant circuit connected to said anode and said point, and means for applying modulating potentials to one of said elements of said discharge device, said space discharge device having high mutual conductance and low plate resistance.

7. A radio frequency circuit comprising, in combination, a source of radio frequency oscillation including an oscillator tube and a piezo-electric crystal for controlling the frequency of the oscillations, a space discharge device having at least an anode, a cathode and control electrode, said source exciting said cathode of the discharge device with respect to a point of reference potential, a load circuit including a series resonant circuit connected to said anode of said discharge device and energized by current appearing between the said anode and the point of reference potential, means for applying a predetermined bias voltage on the control electrode of the discharge device to substantially control the amplitude of the energy fed to said discharge device by said source of radio frequency oscillation, and means for changing the bias voltage for controlling oscillations of said crystal and for applying modulating potentials to said control electrode.

8. A radio frequency circuit comprising, in combination, an oscillator tube having at least a cathode, an anode and a control element, a piezo-' electric crystal included in a regenerative circuit connected between said anode and said control element, an amplifier tube having at least a cathode, an anode and a control element, radio frequencies connecting'means forconnecting the anode of the oscillator tube to the cathode of said amplifier tube, means for connecting the cathode of the oscillator tube to a point of reference potential, a load circuit including a series resonant circuit connected to the anode of the amplifier tube and energized by current appearing between the anode of the amplifier tube and the said point, means for applying a predetermined bias voltage on the control electrode of said amplifier tube to prevent oscillations appearing in said oscillator tube, and means for changing the bias voltage for starting oscillation and for applying modulating potentials to said control electrode.

9. A radio frequency circuit comprising, in combination, a space discharge device having at least an anode, a cathode and control means, a source of carrier frequency for excitin the oathode with respect to a point of reference potential, a load circuit including a series resonant circuit connected to said anode and energized by current appearing between the said anode and said point, means for applying a predetermined bias voltage on the control means, means for adjusting the series resonant circuit at substantially resonance for said predetermined bias voltage, and means for rendering the bias voltage more negative and applying modulating potentials to said control means, thereby modulating into and out of resonance whereby control of the amplitude of the current in the series resonant circuit is obtained.

10. A radio frequency system comprising, in combination, an oscillator circuit including at least an anode electrode and a cathode electrode operating as space discharge means, means for connecting the anode to a point of reference potential, means for exciting the cathode at radio frequency potential above said point, an amplifier circuit including at least a cathode element, an anode element and a' control element operating as space discharge means, radio frequency connecting means for connecting the cathode of the oscillator circuit to the cathode of said amplifier circuit, a load circuit including a series resonant circuit connected to the anode of th amplifier circuit and energized by current appearing between the anode of the amplifier circuit and the said point, and means for applying modulating potentials to the control element of said amplifier circuit.

11. A radio frequency system comprising, in combination, a space, discharge device having at least a first anode, a second anode, a cathode common to both said anodes, a first control grid operating between the first anode and the oathode and a second grid operating between the second anode and the cathode, said first anode and said first grid in combination with said cathode operating as an oscillator, said second anode and said second grid in combination with said cathode operating as an amplifier, said first anode being connected to a point of reference potential, a load circuit including a series resonont circuit connected to the second anode and energized by current appearing between said second anode and said point, and means for applying modulating potentials to the second grid.

12. A radio frequency system comprising, in combination, a first space discharge device having at least an anode, a cathode and a control electrode, a source of carrier frequency for exciting the cathode' with respect to a point of reference potential, means for applying a biasing voltage to the control electrode, a second space discharge device having at least an anode, a cathode and a control electrode, means for connecting the cathode of the second space discharg device to the anode of the first discharge device, a load circuit including a series resonant circuit connected to the anode of the second space discharge device and energized by current appearing between the anode of the second space discharge device and said point, and means for applying modulating potentials to the control electrode of the second space discharge device.

DONALD L. HINGS. 

